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    Subject[PATCH v6 14/21] x86: ptrace: Add function argument access API
    Date
    Add regs_get_argument() which returns N th argument of the
    function call.
    Note that this chooses most probably assignment, in some case
    it can be incorrect (e.g. passing data structure or floating
    point etc.)

    This is expected to be called from kprobes or ftrace with regs
    where the top of stack is the return address.

    Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
    ---
    arch/Kconfig | 7 +++++++
    arch/x86/Kconfig | 1 +
    arch/x86/include/asm/ptrace.h | 38 ++++++++++++++++++++++++++++++++++++++
    3 files changed, 46 insertions(+)

    diff --git a/arch/Kconfig b/arch/Kconfig
    index 76c0b54443b1..4126ad4b122c 100644
    --- a/arch/Kconfig
    +++ b/arch/Kconfig
    @@ -272,6 +272,13 @@ config HAVE_REGS_AND_STACK_ACCESS_API
    declared in asm/ptrace.h
    For example the kprobes-based event tracer needs this API.

    +config HAVE_FUNCTION_ARG_ACCESS_API
    + bool
    + help
    + This symbol should be selected by an architecure if it supports
    + the API needed to access function arguments from pt_regs,
    + declared in asm/ptrace.h
    +
    config HAVE_CLK
    bool
    help
    diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
    index 3b037bc589ab..1ac63d118224 100644
    --- a/arch/x86/Kconfig
    +++ b/arch/x86/Kconfig
    @@ -176,6 +176,7 @@ config X86
    select HAVE_PERF_USER_STACK_DUMP
    select HAVE_RCU_TABLE_FREE
    select HAVE_REGS_AND_STACK_ACCESS_API
    + select HAVE_FUNCTION_ARG_ACCESS_API
    select HAVE_RELIABLE_STACKTRACE if X86_64 && UNWINDER_FRAME_POINTER && STACK_VALIDATION
    select HAVE_STACK_VALIDATION if X86_64
    select HAVE_SYSCALL_TRACEPOINTS
    diff --git a/arch/x86/include/asm/ptrace.h b/arch/x86/include/asm/ptrace.h
    index 6de1fd3d0097..c2304b25e2fd 100644
    --- a/arch/x86/include/asm/ptrace.h
    +++ b/arch/x86/include/asm/ptrace.h
    @@ -256,6 +256,44 @@ static inline unsigned long regs_get_kernel_stack_nth(struct pt_regs *regs,
    return 0;
    }

    +/**
    + * regs_get_kernel_argument() - get Nth function argument in kernel
    + * @regs: pt_regs of that context
    + * @n: function argument number (start from 0)
    + *
    + * regs_get_argument() returns @n th argument of the function call.
    + * Note that this chooses most probably assignment, in some case
    + * it can be incorrect.
    + * This is expected to be called from kprobes or ftrace with regs
    + * where the top of stack is the return address.
    + */
    +static inline unsigned long regs_get_kernel_argument(struct pt_regs *regs,
    + unsigned int n)
    +{
    + static const unsigned int argument_offs[] = {
    +#ifdef __i386__
    + offsetof(struct pt_regs, ax),
    + offsetof(struct pt_regs, cx),
    + offsetof(struct pt_regs, dx),
    +#define NR_REG_ARGUMENTS 3
    +#else
    + offsetof(struct pt_regs, di),
    + offsetof(struct pt_regs, si),
    + offsetof(struct pt_regs, dx),
    + offsetof(struct pt_regs, cx),
    + offsetof(struct pt_regs, r8),
    + offsetof(struct pt_regs, r9),
    +#define NR_REG_ARGUMENTS 6
    +#endif
    + };
    +
    + if (n >= NR_REG_ARGUMENTS) {
    + n -= NR_REG_ARGUMENTS - 1;
    + return regs_get_kernel_stack_nth(regs, n);
    + } else
    + return regs_get_register(regs, argument_offs[n]);
    +}
    +
    #define arch_has_single_step() (1)
    #ifdef CONFIG_X86_DEBUGCTLMSR
    #define arch_has_block_step() (1)
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